Since its introduction to the market in 1962, aromatic polycarbonate has become well known and accepted as a thermoplastic resin suitable for a wide variety of uses including injection molding, extrusion and film formation. The chemistry, synthesis, properties and applications of these polycarbonates are extensively discussed in Chemistry and Physics of Polycarbonates by Schnell, Interscience, 1964 and Polycarbonates by Christopher and Fox, Reinhold, 1962. Although polycarbonates have some inherent flame resistance, being self-extinguishing, ever more demanding requirements of flame-resistance have spawned numerous attempts to increase this property. Two general approaches have been followed. One approach has been to add substantial amounts of halogen, particularly bromine or chlorine, to polycarbonate compositions. The halogen can be carried by polycarbonate polymer chains as in U.S. Pat. Nos. 3,751,400 and 3,334,154 or by a monomeric compound as in U.S. Pat. No. 3,382,207.
However, the presence of substantial amounts of halogen has been found to be detrimental to the properties of the polycarbonate and numerous additives such as those proposed in U.S. Pat. Nos. 3,647,747 and 3,733,295 have been proposed to overcome these detrimental effects. The usage of any of a variety of salts—notably perfluoroalkane sulfonate salts of alkali metal or alkaline earth metal—with and without PTFE as a flame retardant for polycarbonate has been disclosed in U.S. Pat. Nos. 3,775,367; 4,469,833; 4,626,563; 4,626,563; and 4,649,168.
Alkali metal salts of sulfonic acids were disclosed in U.S. Pat. No. 4,469,833 to be flame retardant additives in the context of polycarbonate compositions containing structural units derived from thiodiphenol. U.S. Pat. No. 4,220,583 disclosed flame retardant polycarbonate compositions containing partially fluorinated polyolefin and organic salts of alkali metal or alkaline earth metals. U.S. Pat. No. 3,933,734 disclosed a flame retardant polycarbonate composition comprising metal salts of monomeric and/or polymeric aromatic sulfonic acids. U.S. Pat. No. 3,948,851 disclosed a flame retardant polycarbonate composition comprising metal salts of monomeric and/or polymeric aromatic sulfonesulfonic acids. Flame-retardant, translucent polycarbonate compositions containing partially fluorinated polyolefin, and an organic alkali (or alkaline earth) metal salt were disclosed in U.S. Pat. No. 4,220,583.
Experience has shown that polycarbonate compositions that are imparted flame resistance by the incorporation of sulfonate salts of alkali or alkaline earth metals and fluorinated polyolefin often exhibit an undesirable degree of haze, especially in thick molded articles. This deficiency restricts the amount of flame retardant that may thus be incorporated if optically clear products are desired.